The present invention relates to an image forming apparatus provided with a fixing section for fixing an image formed on a sheet of recording medium in a preceding image forming process by application of heat to the sheet carrying the image.
In modern image forming apparatuses, such as copying machines, printers and facsimile machines, a loose (unfixed) image is first formed on a recording medium (e.g., a sheet of printing paper) and, then, heat is applied to the recording medium to fuse and fix the image to the recording medium. There is a growing demand these days to reduce mounting space of the image forming apparatus. To meet this demand, many image forming apparatuses developed in recent years are of a type in which an image formed of a developing agent, or toner, is transferred onto a sheet of recording medium and the transferred image is fused and fixed to the sheet by application of heat and pressure to the sheet carrying the unfixed image in a fixing section while the sheet is being fed in a sheet feeding direction upward from a sheet feeding section located at a lower part of the apparatus during an image forming process. Then, the sheet carrying the fixed image is redirected and transported generally in a horizontal direction opposite to the sheet feeding direction so that the sheet is discharged to the exterior of the apparatus or sent to an after-treatment unit, or recirculated through a sheet path for double-sided image forming if the apparatus has a duplex copying feature.
This type of image forming apparatus is usually provided with a document reading block (scanner unit) disposed at a topmost part of the apparatus for picking up image information from an original.
To prevent the sheet from deforming (e.g., curling) and toner particles from coming off the recording medium, the sheet should preferably be cooled after the aforementioned heat-assisted image fixing stage. The fixing section could reach high temperature which could potentially cause adverse influence on other parts of the apparatus. To overcome this heating problem, it is usually necessary to make provision for cooling surrounding areas of the fixing section.
There are known some conventional approaches to the resolution of the aforementioned problem. For example, Japanese Laid-open Patent Publication No. 2000-298422 discloses an image forming apparatus having a duct unit which forms an exhaust air channel disposed close to a fuser unit (fixing section) as well as a wall section which blocks flow of air from the fuser unit to the duct unit. This arrangement shown in Publication No. 2000-298422 is intended to prevent a temperature increase within the apparatus housing as a result of outflow of hot air from inside the fuser unit to an internal space of the housing.
Also, Japanese Laid-open Patent Publication Nos. H10-268735 and S60-197561 disclose image forming apparatuses of a type in which each sheet of recording medium is transported generally in a horizontal direction, and a temperature increase within the apparatus is avoided by exhausting air from around a fuser unit (fixing section) to the exterior through a duct or the like.
On the other hand, it is necessary to reduce power consumption of the fuser unit (fixing section) incorporating a relatively high-power heating device as much as possible to meet recent requirements for power savings.
In a case where the unfixed image is fused and fixed to the sheet by application of heat to the sheet of recording medium while the sheet is being transported upward as stated above, masses of hot air formed around the fixing section also ascend in the image forming process. Consequently, there arises a problem that the recording medium once heated in the fixing stage would not easily cool down.
Additionally, an image reading section is often located above the fixing section in the image forming apparatus of the aforementioned type in which the sheet of recording medium is fed upward and, therefore, the image forming apparatus has a problem that its image reading section is likely to reach an abnormally high temperature.
If the interior of the image forming apparatus is cooled by exhausting air masses from around (e.g., immediately above) the fixing section as shown in the aforementioned Patent Publication Nos. 2000-298422, H10-268735 and S60-197561, the fixing section itself is deprived of heat and, as a consequence, there arises a problem that the fixing section (or a heating device) requires an increased amount of power consumption to maintain a specific fixing temperature, despite the need to meet the requirements for power savings.